Client benefits: Based on TWI's knowledge of the role of residual stress in intergranular cracking and the likelihood of failure, the results of the project enabled the client to make an informed decision on whether to replace the affected tubes.

Project background: The safety of nuclear power stations is of paramount importance. TWI was asked for expert advice when primary coolant feeder tubes in a reactor showed intergranular cracking as well as signs of flow accelerated corrosion (FAC). These two factors taken together led to a reduction in the thickness by ~0.1mm per year, resulting in a step profile at the root of the weld increasing the likelihood of failure. TWI's study was based on the assumption that the change in thickness affected residual stresses which in their turn affected the incidence and rate of intergranular cracking.

Solution: TWI's Numerical Modelling and Optimisation team created a 3D weld model of a pipe-to- pipe weld and the results were successfully validated against neutron diffraction measurements. A 3D hub-to-pipe weld model was subsequently set up which predicted the residual stress arising from welding and then thinning.

For more information please contact: nmo@twi.co.uk

Information and advice from TWI and its partners are provided in good faith and based, where appropriate, on the best engineering knowledge available at the time and incorporated into TWI's website in accordance with TWI's ISO 9001:2000 accredited status. No warranty expressed or implied is given regarding the results or effects of applying information or advice obtained from the website, nor is any responsibility accepted for any consequential loss or damage.

Privacy statement | Copyright Statement

TWI Ltd 2008